1. Field of the Invention
Aspects of the present invention relate to a fuel cell system.
2. Description of the Related Art
A fuel cell system is a power system that directly converts energy of a chemical reaction of hydrogen in a hydrocarbon-based material, such as methanol, ethanol, and natural gas, with oxygen into electrical energy. As a clean energy source that can replace fossil energy, the fuel cell has an advantage of producing various ranges of outputs because of a stack structure formed by stacking unit cells, and such a fuel cell has been spotlighted as a small-sized and portable power source since energy density thereof is 4 to 10 times higher than that of a small lithium battery.
However, each unit cell has a different operation state due to deviations during a manufacturing process or uneven dispersion of location, pressure, and temperature of each unit cell in the fuel cell stack. Even though each unit cell has a similar operation state, performance of each unit cell deteriorates differently as the fuel cell system is continuously driven. Further, when performance of a given unit cell is severely decreased during use of the fuel cell stack, the power generation amount of the fuel cell stack is decreased while causing serial performance deterioration of adjacent unit cells so that a life-span of the fuel cell stack is reduced. Therefore, it is important to measure a performance difference between unit cells.
Meanwhile, in order to reduce the production cost of the fuel cell stack, the price of the fuel cell as well as the price of other devices should be decreased. For the cost reduction, a device to measure a performance difference of unit cells can be realized by an integrated circuit, such as an application-specific integrated circuit (ASIC). The ASIC generally requires 4-5V for operation. Conventionally, an operation voltage of the ASIC is supplied from a fuel cell stack; however, the ASIC may not be sufficiently driven by the voltage of the fuel cell stack. For example, a lithium ion battery has a unit cell voltage of about 3V, and when measuring a voltage of 10 unit cells, the voltage of the unit cells becomes greater than 30V so that the ASIC can be sufficiently driven. The configuration of driving the ASIC with the lithium ion battery is disclosed in Japanese Patent Laid-Open Publication No. 2003-70179. However, a voltage of a unit cell of the fuel cell is 0 to 0.8V so the ASIC cannot be sufficiently driven.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.